staging: comedi: ni_tiocmd: introduce ni_tio_acknowledge()

The external callers of ni_tio_acknowledge_and_confirm() only call
this function to ack any pending errors or interrupts before starting
a new async command. Only the internal code in ni_tiocmd uses the
data that is optionally returned by this function.

Remove the export from ni_tio_acknowledge_and_confirm() and introduce
a new exported function that handles passing the NULL params.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>